(1) Field of the Invention
The present invention relates to display devices and fabrication methods for the display devices, and particularly to a display device having a repairable pixel structure and a fabrication method for the display device.
(2) Description of the Related Art
Organic EL displays using organic electro-luminescence elements (hereafter referred to as organic EL elements) have been known as image display devices using current-driven light-emitting elements. Since the organic EL displays have advantages such as good viewing angle characteristics and small power consumption, the organic EL displays have been attracting attention as a candidate for a next-generation flat panel display (FPD).
Usually, the organic EL elements composing the pixels are arranged in a matrix. For example, in an active-matrix organic EL display, thin film transistors (TFT) are provided at crosspoints of scanning lines and data lines, and capacitor units (capacitors) and gates of drive transistors are connected to the TFTs. The TFTs are turned on through selected scanning lines, and data signals from the data lines are inputted to the drive transistors and the capacitor units. With the drive transistors and the capacitor units, the timing of light-emission from the organic EL elements is controlled. With the configuration of the pixel drive circuit, in the active-matrix organic EL display, the organic EL elements can keep emitting light until next scanning (selection). Accordingly, the luminance of the display does not decrease even if the duty cycle increases. However, as typically shown in the active-matrix organic EL display, as the configuration of the drive circuit for light-emitting pixels becomes more complex, and as the number of the light-emitting pixels increases, the number of electric malfunction such as short-circuit or opening of the circuit elements and lines increases in the fabrication process that requires microfabrication.
In particular, in the organic EL panel, the area for the capacitor elements included in the pixel drive circuit is relatively large. As a result, the capacitor elements are susceptible to the influence of particles and others between electrodes, causing an increased pixel malfunction rate due to malfunction such as short-circuit.
The short-circuit in the capacitor element can be repaired by disconnecting the capacitor unit from other normal part by laser irradiation and current supply. A pixel circuit provided with a backup capacitor element has been developed in order to prevent a change in the pixel characteristics due to reduced capacitance by separating the malfunctioning capacitor unit has been developed.
FIG. 13 is a circuit diagram illustrating a part of the screen of the liquid crystal display device disclosed in the patent literature 1: Japanese Unexamined Patent Application Publication No. 2003-15549. FIG. 12 illustrates a circuit configuration of the display unit in which pixels are arranged in a matrix. The display unit includes a scanning line 501 and a capacitor line 502 which are arranged for each row of the pixels, and a signal line 503 provided for each column of pixels. Each pixel includes a pixel TFT 504, capacitor elements 505a and 505b which are connected in parallel (505a and 505b have an approximately the same capacitance value), a pixel electrode 520, a common electrode 506, and a liquid crystal element 507, and a capacitor element 508 for repair is provided together with the capacitor elements 505a and 505b. The capacitor element 508 is arranged to have a capacitance value approximately same as the capacitor element 505a (or 505b), and is usually separated from the pixel electrode 520.
In the configuration described above, for example, as the pixel at the center of FIG. 13, the capacitor element 505b is short-circuited due to the dust during the fabrication process. Without any adjustment, the pixel electrode 520 is directly connected to the capacitor line 502. Consequently, voltage is not applied to the liquid crystal element 507, causing pixel defect. Thus, the disconnect-able portion 510 is disconnected by laser irradiation, and laser contact is performed on the connectable portion 511. At the connectable portion 511, two types of lines are overlapped opposite to each other via the interlayer insulating film, and the two types of lines are connected by the laser irradiation on the overlapping part. With this, even when the capacitor element 505b is short-circuited, it is possible to disconnect the capacitor element 505b, and to connect the capacitor element 508 for repair.
With the configurations of the disconnect-able portion 510 and the connectable portion 511 and the laser irradiation on them, it is possible to repair the pixel to a normal state even if part of the capacitor element in the pixel circuit is short-circuited, without reducing the capacitance held by the repaired pixel.